Virulent Newcastle Disease Virus 

(vNDV)

Case Definition

1. General disease/pathogen information

Newcastle disease (ND) is a contagious and often fatal disease that affects over 250 bird species 

that is caused by infection with virulent strains of Newcastle disease virus (vNDV). Clinical signs 

vary and can include respiratory, neurological, reproductive, and intestinal signs. The severity of 

disease produced varies with the host species and the strain of the virus, with chickens being 

the most susceptible and waterfowl the least susceptible. In humans, the virus causes a 

temporary mild conjunctivitis and influenza-like symptoms. The World Organization for Animal 

Health (OIE) has defined ND (historically called Exotic Newcastle disease [END] in the United 

States) as an OIE-notifiable disease, based on its potential for rapid spread, serious economic 

consequences, and impact on the international trade of poultry and poultry products.

1.1. Etiologic Agent: Newcastle disease virus is a negative-sense, single-stranded RNA virus 

also known as avian paramyxovirus-1 (APMV-1). It is a member of the family 

Paramyxoviridae, genus Avulavirus. There are many different serotypes of avian 

paramyxovirus, with APMV-1 being the most important for poultry. APMV-1 viruses are 

categorized into five pathotypes according to the OIE, which characterize virulence as 

well as tropism: asymptomatic (no apparent disease), lentogenic (low virulence 

viruses), mesogenic (moderate virulence), and viscerotropic vs neurotropic velogenic 

(virulent) based upon pathogenicity experiments performed in chickens. While these 

definitions remain important descriptors, APMV-1 viruses are currently reported in the 

U.S. as either low virulent (e.g. lentogenic viruses) or virulent (comprising mesogenic 

and velogenic viruses). The OIE defines Newcastle disease as an infection with a vNDV

characterized by either an intracerebral pathogenicity index (ICPI) of 0.7 or greater in 

day-old chickens, or the presence of multiple basic amino acids at positions 113- 116 of 

the C-terminus of the fusion (F2) protein (either arginine (R) or lysine (K)), plus 

phenylalanine (F) at residue 117 of the F1 protein.

1.2. Distribution: ND is endemic in a number of countries in Asia, Africa, and the Americas. 

Commercial poultry in the U.S. and Canada are free of vNDV. Outbreaks of vNDV 

occurred in California, Nevada, and Arizona in 2002-2003 and in Texas in 2003. Virulent 

NDV has not been detected in U.S. commercial poultry since 2003.

1.3. Clinical signs: Clinical signs can vary significantly from high levels of morbidity and 

mortality to sub-clinical infections depending on viral strain, host species, age of host, 

co-infection with other organisms, physiologic and environmental stress, and immune 

status. General clinical signs include respiratory distress, decreased egg production, 

depression, neurological signs, and diarrhea.

Animal and Plant 

Health Inspection 

Service

Veterinary 

Services

May 24, 2018
Case Definition for Virulent Newcastle Disease Virus

USDA APHIS VS - 2

1.3.1. Chickens: Chickens are one of the most susceptible species to disease caused by 

vNDV infection. Poorly protected or unprotected flocks infected with vNDV 

typically experience high death losses within 24-48 hours with no apparent 

clinical signs. Birds that survive beyond 12-14 days may experience permanent 

neurological signs and/or permanent reproductive impairment. Vaccinated birds 

often experience marked drops in egg production with eggs that are misshapen, 

abnormally pale, rough, or thin-shelled with watery albumin. Infections with low 

virulent strains typically cause respiratory signs, decreased feed and water 

consumption, and a small decline in egg production.

Virulent strains may be viscerotropic or neurotropic. Viscerotropic strains cause 

hemorrhagic lesions in the intestinal tract, with conjunctival edema (at 2-3 days) 

and depression, and may result in sudden death regardless of vaccination 

status. Infection with neurotropic strains causes neurologic signs such as 

muscular tremors, leg and wing paralysis, torticollis, and opisthotonos, with 

death after 5-7 days. It is important to note that viscerotropic strains may also 

cause neurologic signs such as muscle tremors and torticollis; however, 

neurotropic strains rarely cause gastrointestinal hemorrhagic lesions in absence 

of other pathogens. 

1.3.2. Turkeys: In general, turkeys tend to be less susceptible to APMV-1 infections. 

When infected, they may experience high morbidity, but clinical disease is less 

severe and mortality is lower.

1.3.3. Other birds: Upland game birds occasionally have severe clinical signs when 

affected with vNDV. Psittacine species exhibit variable susceptibility to vNDV 

and have the potential to chronically shed virus. 

1.3.4. Species-adapted strains: APMV-1 viruses from pigeons are variants referred to 

as pigeon paramyxovirus-1 (PPMV-1). While these viruses typically have virulent 

fusion cleavage sites, chickens infected with PPMV-1 demonstrate variable 

clinical disease; however, if found in poultry, these viruses are reportable under 

the current OIE definition. A species-adapted virus is also found in double 

crested cormorants. These lineages are distinguishable by genomic sequence.

1.4. Incubation period: The incubation period in poultry ranges from 2-15 days with an 

average of 2-6 days in chickens infected with virulent strains. Time until disease onset 

depends upon host species, viral strain and dose, age and immune status of the host, 

presence of other infections, and environmental conditions. 

1.5. Differential diagnosis: The differential diagnosis for Newcastle disease includes other 

causes of septicemia, enteritis, respiratory disease, and/or neurological disease.

1.5.1. Viral diseases: highly pathogenic avian influenza, laryngotracheitis, fowl pox 

(diphtheritic form), Pacheco’s disease, avian metapneumovirus, infectious 

bronchitis. 

1.5.2. Bacterial diseases: fowl cholera, psittacosis (chlamydiosis), mycoplasmosis, 

salmonellosis (especially in pet birds), botulism (especially in cormorants) 

1.5.3. Other: aspergillosis, management errors such as deprivation of water, feed, air
Case Definition for Virulent Newcastle Disease Virus

USDA APHIS VS - 3

1.6. Transmission and reservoir: Transmission can occur directly and indirectly from 

infected birds to susceptible birds. Infection can occur through direct contact with fecal 

excretions and respiratory secretions of infected birds. Contaminated feed, water, 

premises, and other fomites allow for indirect transmission. Vaccinated poultry may 

serve as a source of transmission if acutely infected and introduced to a susceptible 

flock. Virus can be shed throughout the incubation period and into convalescence. 

Illegally imported psittacine species, some of which may not show clinical signs, have 

served as sources of vNDV infection to domestic poultry. Survival of NDV in the 

environment is prolonged from days to months in the presence of organic matter, and 

up to years in feather follicles or temperatures <0C. However, the virus is destroyed 

rapidly by dehydration and by the ultraviolet rays in sunlight.

1.7. Epidemiology: Morbidity of unvaccinated chickens infected with vNDV strains can 

reach 100 percent, and mortality ranges from 70-100 percent. Many other avian 

diseases present with clinical signs similar to vNDV; therefore, laboratory testing is 

necessary to distinguish between diseases. The virulence of the affecting strain is also 

important and OIE-designated assays should be performed to determine virulence of 

vNDV; virulent strains can be maintained in pigeons and cormorants. Viruses of low 

virulence may be detected as US poultry are typically vaccinated with live NDV vaccines 

and other low virulence viruses may circulate in wild birds, especially wild waterfowl.

2. Laboratory criteria: OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 

2018, Chapter 2.3.14. Newcastle Disease. 

2.1. Agent isolation and identification: Samples of choice are tracheal, oropharyngeal, or 

cloacal swabs (or feces) from live birds. From dead birds, tissues (lung, spleen, trachea, 

intestine, and brain) as well as pools of organs and feces, are appropriate specimens. 

Tests include the isolation or culture of the virus in embryonated chicken eggs 

(appropriate cell culture may be used per the OIE Manual of Diagnostic Tests), and realtime reverse transcriptase polymerase chain reaction (rRT-PCR) for detection of the 

virus or the viral genome. Viral isolates can be identified by the hemagglutination (HA), 

hemagglutination inhibition (HI), and real-time reverse transcriptase polymerase chain 

reaction (rRT-PCR) tests. APMV-1 viruses, especially those with moderate to high titers, 

may cross-react in the HI tests with other APMV viruses, most specifically APMV-2, -3, 

and -7.

2.2. Pathogenicity Assessment: The intracerebral pathogenicity index (ICPI) in 24-40-hourold chicks from specific pathogen free (SPF) eggs is the definitive assessment for 

virulence per OIE. The OIE allows for confirmation of virus virulence by amino acid 

sequence analysis of the fusion protein cleavage site, but molecular methods are not 

sufficient evidence for lack of virulence.

2.3. Serological tests: Use clotted blood or serum for enzyme-linked immunosorbent assay 

(ELISA) or HI. Antibodies are detectable 6 to 10 days after infection. 
Case Definition for Virulent Newcastle Disease Virus

USDA APHIS VS - 4

3. Case definition: 

3.1. Suspect case: Domesticated bird or flock having:

3.1.1. Clinical signs compatible with ND; OR

3.1.2. Detection of APMV-1 by rRT-PCR; OR

3.1.3. Epidemiological information indicating exposure to vNDV.

3.2. Presumptive positive case: A suspect case (as in 3.1) with detection of vNDV by the 

fusion-target rRT-PCR test at a laboratory designated by the Secretary of Agriculture; 

NOTE – a negative virulent test in the face of clinical signs requires further virus 

characterization by sequence and/or in vivo testing. 

3.3. Confirmed positive case: Domesticated bird or flock from which:

3.3.1. vNDV has been identified at the National Veterinary Services Laboratories 

(NVSL) by: 

3.3.1.1. Presumptive positive (as in 3.2) with confirmation of multiple basic amino 

acids (either directly via protein or by deduction through sequencing) in 

the fusion gene at the C-terminus of the F2 protein and phenylalanine at 

residue 117, which is the N-terminus of the F-1 protein. The term ‘multiple 

basic amino acids’ refers to at least three arginine or lysine residues 

between residues 113 and 116; AND/OR

Failure to demonstrate the characteristic pattern of amino acid residues as 

described above would require virus isolation and further characterization 

by an in vivo test.

3.3.1.2. The vNDV has an ICPI in day-old chicks (Gallus gallus) of 0.7 or greater. 

4. Reporting criteria: Virulent ND is a U.S. foreign animal disease (FAD) and OIE-notifiable 

disease. OIE reporting is limited to infections in poultry as defined by the OIE.1Follow

standard FAD procedures according to Veterinary Services Guidance Document 12001 

(formerly VS Memorandum No. 580.4). Suspect cases reported to State Animal Health 

Official or Assistant District Director (ADD).

 

1

OIE definition of poultry: all domesticated birds, including backyard poultry, used for the production of meat or eggs 

for consumption, for the production of other commercial products, for restocking supplies of game, or for breeding 

these categories of birds, as well as fighting cocks used for any purpose.

Birds that are kept in captivity for any reason other than those reasons referred to in the preceding paragraph, 

including those that are kept for shows, races, exhibitions, competitions or for breeding or selling these categories of 

birds as well as pet birds, are not considered to be poultry.
Case Definition for Virulent Newcastle Disease Virus

USDA APHIS VS - 5

References:

1. Foreign Animal Diseases. The United States Animal Health Association. Seventh Edition. 

2008.

2. Iowa State University: Center for Food Security and Public Health. Newcastle Disease. 

Available online at www.cfsph.iastate.edu/Factsheets/pdfs/newcastle_disease.pdf

3. Merck Online Veterinary Manual. Newcastle Disease in Poultry. Available online at

http://www.merckmanuals.com/vet/poultry/newcastle_disease_and_other_paramyxov

irus_infections/newcastle_disease_in_poultry.html?qt=newcastle disease&alt=sh

4. OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2018. Chapter 

2.3.14. Newcastle Disease. Available online at

http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.03.14_NEWCASTLE

_DIS.pdf

5. OIE Terrestrial Animal Health Code 2018. Chapter 10.9. Newcastle Disease. Available 

online at http://www.oie.int/index.php?id=169&L=0&htmfile=chapitre_nd.htm